 This means playing the note a semitone above or below one of the chord tones.In the key of C, the notes in the tonic chord are C(1st or root of chord), E(3rd), G(5th), and B(7th).So by playing an E flat at the end of a line then resolving (moving up a semitone) to an E, this would be one basic example of targeting and would be targeting the third of the chord (E).